The present invention relates to both electrostatic and electromagnetic treatment of fluid systems and more particularly to the construction and operation of water treating devices having electrostatic fields, electromagnetic fields, and micro-particle filtering to remove both particulate and biological materials from the water flowing within the system. The word “water”, as used herein, means water complexes containing dissolved and suspended solids, biological materials, etc., as are normally found in a great many industrial and commercial applications.
Industrial water cooling systems, including heat exchangers and water cooling towers, are examples of closed-loop and open loop recirculating systems that are susceptible to water complex contamination and fouling, as well as the buildup of scale or corrosion along the inner surfaces of the water conduits with the reduction of thermal transfer properties due to increased levels of particulate and biologic materials contained in the water stream and on the container surfaces. Closed recirculating systems use heat exchangers and circulate water in a closed loop with negligible evaporation to the atmosphere. Heat is transferred from a process system to the closed cooling water loop by heat exchange equipment and removed from the closed system loop by a second exchange of heat for cooling in an open recirculating system, commonly a water cooling tower open to the environment. Most chilled water systems will incorporate an open recirculating cooling water system with a cooling tower for condenser cooling.
Cooling water systems are subject to a variety of contaminants that can interfere with heat transfer, increase corrosion rates, restrict water flow, and cause loss of process efficiency and production. Customized scale inhibitor programs have been deemed necessary by existing industry recommendations for the prevention of mineral scales including calcium carbonate, calcium sulfate, calcium phosphate, magnesium silicate, and other silica compounds, and mixtures of these, and sludge and organic particulates including silt and windblown debris, biological deposits, metallic oxides, corrosion products, and other contaminants. Mineral scales form when dissolved solids and minerals are introduced to a cooling water system through a raw water source or as a result of airborne contamination. These dissolved solids precipitate when the solubility levels are exceeded due to increased concentrations, elevated water temperature, and higher pH levels. Sludge and organics form when suspended material (by-products of corrosion, dust, sand, microbial growth, and minerals) are introduced through influent water or airborne impurities.
These conditions have been historically treated with some form of chemical to either inhibit or disperse the water system contaminant. The function of a dispersant, or antifoulant, is to prevent the agglomeration of solids and their accumulation on critical surfaces. Materials that handle these potential deposits have been referred to in the industry as dispersants, polymers, penetrating agents, deposit control materials, polyectrolytes, crystal modifiers, antifoulants, sequestrants, mineral stabilizers, antiscalants, surfactants, mud removers, and emulsifiers, all of which are introduced into the fluid stream as some form of chemical additive.
Another problem that exists in cooling systems using a water complex as a coolant is the occurrence of corrosion along the fluid conduit internal surfaces. Such corrosion can be caused by dissolved oxygen in the water, precipitation of insoluble minerals, the breakdown of anti-freezing compositions, e.g., glycolic acids, and bacterial contamination. Corrosion inhibitors are designed to prevent metal loss along the fluid conduit and on metal containment surfaces that would otherwise lead to critical system failures in heat exchangers, recirculating water piping, and process cooling equipment. Moreover, corrosion will result in a loss of thermal efficiency as corrosion products precipitate on critical heat transfer devices and create an insulative deposit on the metal heat exchange surfaces.
Corrosion may be caused by metals attempting to return to their natural state. Corrosion can be present in many forms including uniform metal loss, localized or pitting, bimetallic, galvanic, and microbiological induced corrosion. The process starts when surface irregularities, stresses, or compositional differences result in the formation of a corrosion cell (anode and cathode). Once started, corrosion at the anode causes metal to be released into the system or re-deposited locally. Pitting is particularly problematical because the local loss of metal can result in through-wall perforation of piping and tubing.
The industry has treated water cooling systems with a number of corrosion inhibiting chemicals that fall into three classes: organic, inorganic, and non-phosphate corrosion inhibitors. These products are engineered to passivate metals by reducing the corrosion potential associated with the anode and cathode of the corrosion cell. Chemicals that form protective films at the anode include chromate, orthophosphate, nitrite, silicate, and molybdate. Chemicals that form films on the cathode include calcium carbonate, polyphosphate, zinc, phosphonate, and a number of azoles.
The three most reliable corrosion inhibitors for closed cooling water systems are chromate, molybdate, and nitrite materials. Generally, the chromate or molybdate types have proven to be superior treatments. For mixed metallurgy systems, the molybdate inhibitors provide the best corrosion protection. Chromate treatments in the range of 500-1000 ppm as Cr4O2− are satisfactory unless bimetallic influences exist. When such bimetallic couples as steel and copper are present, chromate treatment levels are recommended to be increased to exceed 2000 ppm. Maximum inhibitor effectiveness can be achieved if the pH of these systems is kept between 7.5 and 9.5.
In a closed system, it can be quite difficult to prevent corrosion of aluminum and its alloys; the pH of the water must be maintained below 9.0. Aluminum is amphoteric as it will dissolve in both acids and bases, and its corrosion rate accelerates at pH levels higher than 9.0. The bimetallic couple that is most difficult to cope with is that of copper and aluminum, for which chromate concentrations even higher than 5000 ppm may not be adequate. Also, where circulating pumps are equipped with certain mechanical seals, such as graphite, chromate concentrations may not exceed 250 ppm. This is due to the fact that water leaking past the seals evaporates and leaves a high concentration of abrasive salts that can damage the seal. Another problem is encountered when chromate inhibitors are used in cooling systems serving compressors that handle sour gas. If sour gas leaks from the power cylinder into the water circuit, significant chromate reduction will occur, causing poor corrosion control and deposition of reduced chromate. In view of the stated problems, treatment of the water with corrosion inhibitors in the form of chemicals compositions is not a complete resolution of the problem.
In very high heat transfer rate applications, such as continuous caster mold cooling systems, chromate levels should be maintained at 100-150 ppm maximum. Under these extreme conditions, chromate can accumulate at the grain boundaries on the mold, causing enough insulation to create equipment reliability problems. The toxicity of high-chromate concentrations may restrict their use, particularly when a system must be drained frequently. Current legislation has significantly reduced the allowable discharge limits and the reportable quantity for the spill of chromate-based products. Depending on the type of closed system and the various factors of State/Federal laws limiting the use of chromate, a non-chromate alternative may be needed.
Molybdate treatments provide effective corrosion protection and an environmentally acceptable alternative to chromate inhibitors. Nitrite-molybdate-azole blends inhibit corrosion in steel, copper, aluminum, and mixed-metallurgy systems. Molybdates are thermally stable and can provide excellent corrosion protection in both soft and hard water. System pH is normally controlled between 7.0 and 9.0. Industry recommended treatment control limits are 200-300 ppm molybdate as MoO42−. However, Molybdate inhibitors are not recommended to be used with calcium levels greater than 500 ppm.
Nitrite is another widely accepted non-chromate closed cooling water inhibitor. Nitrite concentrations in the range of 600-1200 ppm as NO2− will suitably inhibit iron and steel corrosion when the pH is maintained above 7.0. Systems containing steel and copper couples require treatment levels in the 5000-7000 ppm range. If aluminum is also present, the corrosion problem is intensified, and a treatment level of 10,000 ppm may be required. In all cases, the pH of the circulating water should be maintained in the alkaline range, but below 9.0 when aluminum is present. When high nitrite levels are applied, an acid feed may be required for pH control. One significant drawback to nitrite treatments is the fact that nitrites are oxidized by microorganisms. Denitrifying bacteria can consume the chemical inhibitor, reducing the protection on the fluid system's conduit and containment surfaces, which can lead to low inhibitor levels and biological fouling. Slime producing bacteria can accelerate such fouling. The feed of non-oxidizing antimicrobials may be necessary to control nitrite reversion and biological fouling. In addition, sulfate reducing bacteria and iron reducing bacteria produce acids that can cause thinning and ultimately holes through the inner surfaces of the walls of pipes, tubes and coils. In view of all of the above, it is clear that the use of one chemical can create a myriad of problems requiring other chemicals to correct. Further, with the strict limitations of chemical concentrations due to the use of certain metals in the conduit and containment systems, chemical usage is significantly inhibited.
As part of the closed loop system, heat exchangers are utilized to remove unwanted heat from an industrial process and typically transfer the thermal energy to a recirculating cooling water stream. The temperature of cooling water will be elevated as it absorbs heat from the process side, which is then expelled through partial evaporation of the water across a cooling tower. Several problems may arise in this heat transfer process as issues like corrosion, scale, fouling, and microbial growth will reduce flow rates and heat transfer rates and lower system efficiency. Heat exchangers are generally of three different designs including: shell and tube, plate and frame, and exposed tube. Chemical treatments to alleviate and remove the associated problems noted above have long been used in the industry with mixed results.
Open recirculating systems provide the most common form of industrial and commercial cooling, continually recycling and reusing the same water to cool process equipment. In these systems, water, after leaving the cooling tower, is pumped to industrial and/or commercial applications using heat exchangers, condensers, air compressor jackets, or process reactors. In this cycle, the water returning to the cooling tower water has absorbed excess heat from the manufacturing or alternative process which is then dissipated by spraying the water through a water cooling tower where partial evaporation takes place. The cooling tower exposes the heated water to air, causing a small percentage of the water to evaporate, which removes a substantial amount of heat in the process. The water that doesn't evaporate is cooled and then reused.
Reusing chemically treated cooling water results in not only water savings, but chemical savings as well, as the chemistries are retained in the system. However, problems associated with corrosion, deposition, and microbial growths become more severe for several reasons. First, the process of evaporation concentrates the amounts of dissolved and suspended solids in the circulating water, leading to corrosion of conduit and containment surfaces and deposition of materials within the conduit flow stream. Secondly, the warm temperatures in open recirculating cooling towers results in significant biological growth. Lastly, the operation of a water cooling tower exposes the water to air and as a result airborne contaminants are absorbed that may be the cause of additional corrosion and microbial growth.
For many years the industry has treated these problems with a variety of chemical treatments as discussed above. Even though cooling towers have a number of designs including natural draft, mechanical, cross flow, and counter-flow the industry has responded to each of the designs with not less, but more chemical treatments. The chemical treatments are used to increase heat transfer efficiency by eliminating fouling within heat transfer piping with scale inhibitors by chemically preventing fouling that result from the precipitation of constituents, the settling of suspended matter, and microbial growth. Although, the corrosion inhibitor chemical treatments may reduce maintenance and plant or facility downtime by keeping metals within the system from losing thickness, which cause system failures and reduce deposition caused by corrosion, they require continual monitoring and reintroduction as the chemistries are subject to reaction with the water and containment surfaces and to microbial oxidation. This will result in increased temperature differential in the cooling tower water due to the introduction of biocides to reduce the number and growth of microorganisms on cooling tower fill seeking to increase the splash effect for maximizing the air contact with the water and increase evaporation rates.
Another type of coolant water treatment is a non-chemical treatment of water complex systems. The non-chemical treatment has been the use of electric current within and without the conduits carrying the fluid flow. Apparatus for the treatment of moving liquid by causing electric current flow or discharge therein and/or impressing electrically induced fields there across have been known for many years, but the application of such devices to common industrial and commercial problems, such as water system scaling and clogging, has only been met with varying success. Some installations have appeared to be functional while others which seemed to be operating under generally similar circumstances obviously failed and no broadly accepted reasons for the different results have been advanced. The optimum type, size and characteristics of a treatment system to produce desired and reliable results in a particular environment appear to have been unnecessarily limited with respect to DC voltage imposed on the electrostatic field.
One predictive method for water treatment was disclosed in U.S. Pat. No. 4,073,712 in which a positively charged, axially placed conduit electrode insulated by a dielectric material provides an electrostatic field through the flowing water in the conduit, with a negatively charged electrode around the conduit, thereby providing a three capacitor system. This early system was further advanced with the devices and methods of U.S. Pat. Nos. 6,294,137 and 6,652,715 that increased the voltage of the electrostatic field to at least 10,000 volts dc and up to in excess of 40,000 volts dc with an extremely low power of approximately 5 watts. Based upon the experiences of the reversed polarity of the electrodes and the increased voltage range, differing lengths of the electrode within the conduit are selected in the range of 18 to 36 inches with the particular length dependent upon flow rates, particulate concentration in and polarity of the liquid, the degree of required particulate non-aggregation or surface adhesion, and other related variables.
As can be seen from the foregoing discussion, a large number of factors and complex interactions are involved in the treating process to remove both particulate and biologic material from the liquid cooling stream. This seems logical since such liquid systems are themselves usually highly complex, including variations in dissolved salts, suspended solids, turbulence, pH, piping, electrical environment, temperature, pressure, biologic elements, etc. Many liquid clogging mechanisms, including water system scaling, involve the electrostatic relations between suspended particles, the carrier liquid and the walls of the piping network.
Thus, an electrostatic field effectively developed across a section of flowing water primarily affects not only the water, but mainly suspended, especially colloidal size, particles immersed in the water. The effect of the field will depend, in large measure, upon the relationship of the natural electrostatic charge on such immersed particles to the electrostatic charge on the various surfaces of the treating apparatus and how the latter charge induces a response on the liquid contacting surfaces of the piping network. If relative conditions are proper, the particles will be urged by the field to remain in suspension or migrate toward a charged electrode isolated from the walls of the piping network, thus reducing the tendency to form flow restricting deposits on the inner surface of the conduit. The reduction of colloid particles which are capable of acting as seeds for nucleation of scale building crystal formations results in a reduced tendency for scale deposition.
The natural electrostatic charge on the immersed particles in the liquid, or more accurately, the overall charge effect of the various groups of particles normally associated in the same system, can be determined by known procedures, but the control of the electrostatic charge in critical treater surfaces has been heretofore very limited due to the configuration of the electrodes. One aspect of the present invention continues the reversal of the decades old method of fabricating conduit electrostatic field treatment devices. This is accomplished by locating the positive, ground electrode situated generally within the axial space of the conduit at or near a right angle inlet/outlet flow point, where the conduit inner surface serves as the negatively charged electrode such that the liquid flowing in the conduit becomes negatively charged for later process advantage. The precise placement of the in-flow electrode will be described with greater particularity below.
The electrostatic field between particular water treater surfaces, in large part, can be predicted and controlled by limiting certain parameters in treater construction and installation including the dielectric constant of the insulating material or materials in contact with the water, the efficiency of the insulating material or materials and seals in preventing charge leakage, and the physical size ratio of the treater parts which form the surfaces producing the electrostatic field across the water complex under treatment.
However, the in-flow electrode water treater is only one of several sub-systems to accomplish the multi-phase treatment of the water system by the present invention. With the addition of a series of in-flow electrodes along with the altering of the configuration of the electrode from a single pole to a dual pole immersed in the liquid flow enhances the electrostatic treatment effect. Also, altering the type of metal used in the electrodes selected for the elimination of biologic materials such as bacteria and minute plant life further enhances the electrostatic treatment effect. Two of these modified electrodes coupled with a magnetic/ion charging electrode placed within a series of ionizing cells have been determined to substantially, if not completely, eliminate biologic materials from recirculating through the liquid flow system.
The dissolved and suspended particulate materials, as well as the biologic materials, are also passed through a series of filtering vessels that cause the separation of the dissolved and suspended solids from the liquid flow for particles approximating one micron in size or larger. Each of the filtering vessels creates a flow path that will create turbulence in the water such that the particulate material will precipitate downward due to gravity when blocked by flow limiting barriers. The number of filtering vessels that are required is dependent upon the application, i.e., the quantity of coolant water flowing past a fixed point and the flow rate of the water, with the number usually falling in the range of from two to six filter vessels being utilized.
The principal objects of the present invention are: to provide operable and efficient multi-phase water treatment systems including the use of electrostatic water treaters and mechanical filtering; to provide such treaters which function to predictably inhibit the formation of scale from colloidal particles immersed in flowing water; to provide a treater construction which substantially reduces the formation of scale in piping systems and may function to remove scale already formed; and to provide a water complex treater construction which substantially reduces biologic materials such as bacteria and minute plant life, e.g., algae, slime, etc. contained in the flowing water. It is another object of the present invention to cause the precipitation of suspended particles out of the water complex and to manage any dissolved solids contained therein by reducing particulate materials contained within the water complex, precipitate such particulate materials for collection, and remove them entirely from contact with the continuing flow of the water complex.
It is also an object of the present invention to provide a method of designing operable and efficient multi-phase water treatment systems for particular installations and to provide a method of treating water to reliably inhibit the formation of certain clogging deposits in the piping system containing the same. It is a further object of the present invention to provide a dependable alternative to many types of chemical water treatment for water systems and to provide such methods and apparatus which have wide application in improving desired properties of water systems for industrial and residential purposes at minimal cost and maximum safety.
Other objects will appear hereinafter.